Historical Patterns in Lichen Communities of Montane Quaking Aspen Forests

Document Type

Contribution to Book

Journal/Book Title/Conference

Advances in Environmental Research

Volume

15

Editor

Justin A. Daniels

Publisher

Nova Science Publishers

Publication Date

2011

First Page

33

Last Page

64

Abstract

Climate shifts and resource exploitation in Rocky Mountain forests have caused profound changes in quaking aspen (Populus tremuloides Michx.) structure and function since Euro-American settlement. It therefore seems likely that commensurate shifts in dependent epiphytes would follow major ecological transitions. In the current study, we merge several lines of inquiry to investigate historical changes using lichens as bioindicators of forest structure, air quality, and community composition. Though lichens are well known for their sensitivity to air borne pollutants, recent utilization in the monitoring realm has lead to novel uses as indicators of biodiversity and stand composition. A landscape level investigation in northern Utah and southern Idaho, USA, was implemented to track contemporary and long-term impacts of humans on aspen forests and their dependent macro lichens. We use historical sources, climate data, fire records, and passive ammonia sensors alongside forest and lichen monitoring techniques to gain further insight into aspen and epiphytic lichen community change over the past 150 years. Our research shows that historic drought conditions correlated closely with pulses of aspen regeneration during this period. Aspen initiation was closely aligned with large-scale resource impacts of the late 19th century. During the 20th century a moist climate pattern generally favored shade-tolerant conifers. Additionally, results from nonmetric multidimensional scaling (NMS) ordination indicate a primary successional gradient in determining lichen communities, but also revealed a significant gradient of more recent impacts from nitrogen loading originating from local ammonia (NH3) sources. While advancing succession generally favors lichen diversity, our findings suggest that medium-distance transport (10-50 km) of local air pollutants is already contributing to altered lichen communities. Overall, there are strong ties between landscape-level disturbance history and present aspen-dependent species assemblages. Effects on the epiphytic community are viewed as symptomatic of greater biodiversity and ecosystem impacts.

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